Loudspeaker enclosure with enhanced bass response

ABSTRACT

A loudspeaker enclosure comprises a housing defining therein a principal volume having a front wall and a substantially smaller minor volume. The minor volume has a rear wall common to the front wall of the principal volume. The common wall defines a port which communicates the minor volume to the principal volume. A speaker mounting opening is defined in a front wall of the minor volume. The speaker mounting opening defines the only opening from the exterior of the housing to the interior thereof.

.Iadd.This is a continuation of application Ser. No. 212,986, filed Dec.4, 1980, now abandoned. .Iaddend.

FIELD OF THE INVENTION

This invention pertains to loudspeaker enclosures. More particularly, itpertains to loudspeaker enclosures having enhanced freedom fromresonance over a large range of frequencies generally in the bassfrequency range.

BACKGROUND OF THE INVENTION

Review of the Prior Art

Loudspeaker enclosures designed for reproducing relatively low audiofrequencies, i.e., in the range from about 100 hertz and below, havelong been subject to objectionable resonances within the frequencyranges of their operation. For the purposes of this invention, a bass orlow frequency loudspeaker or loudspeaker enclosure, is one intended toreproduce sound in the range of from about 250 hz and below down to thelower limit of the human hearing range which is in the neighborhood of15-25 hz., depending upon the individual.

The problem encountered with a typical bass loudspeaker and itsenclosure is that the combination tends to resonate at one or morepoints in the frequency range in which it is operated. These resonancesresult in boominess of the speaker, which boominess is sometimespreferred but which, nevertheless, is not consistent with faithfulreproduction of the sound intended. For example, a typical bassloudspeaker enclosure is used to reproduce music in combination withmid-range and high frequency loudspeakers and enclosures therefor, ineither a home or commercial audio system. In such a system the sound isrecorded either on a phonograph record or on magnetic tape. The lowerfrequency sounds, as heard by a user of the system, are accentuated atsome frequencies as compared to the relative volume of the sounds forthose frequencies as recorded on the record or tape.

Great care is taken in the modern recording industry to cause the soundrecorded on a phonograph record or tape to correspond, in frequency andvolume, as faithfully as possible to the sound of the performancereproduced in the recording. Similarly, modern electronic audioequipment (amplifiers and the like) are extremely linear over theiroperating ranges and faithfully amplify and present to the loudspeakerselectrical signals which similarly faithfully correspond to the soundgenerated in the performance embodied in the phonograph or taperecording. The presence of resonances in the loudspeaker system used totransduce the electrical output of the audio amplifier to an audiblesignal is at odds with and subverts the care taken in the originalrecording and in the reproduction amplifiers. These resonances are duein part to resonance effects in loudspeakers, but more importantly, as Ihave discovered, to resonances within the loudspeaker enclosuresthemselves. I have found that low frequency loudspeakers are verysimilar to each other in overall performance characteristics in respectto resonances, and that the more expensive low frequency loudspeakersnow commercially available show only a small improvement in resonancecharacteristics as compared to the lower priced low frequency speakerscommercially available.

That is, in the combination of a low frequency loudspeaker and anenclosure therefor, I have identified the enclosure, rather than theloudspeaker, as the principal source of resonances in the range ofaudible sound which the loudspeaker is used to reproduce in an overallaudio reproduction system. A need therefore exists for an improvedloudspeaker enclosure which, when used in combination with a lowfrequency loudspeaker, reproduces sound over the intended frequencyrange without objectionable resonances at one or more frequencies withinsuch range.

SUMMARY OF THE INVENTION

This invention provides an improved loudspeaker enclosure which isparticularly useful in the reproduction of sound in the bass or lowfrequency range. I have found that the present loudspeaker enclosureconfiguration is also useful to provide improved reproduction ofso-called mid-range audio frequencies, but in these frequencies theimprovements provided by this invention over the prior loudspeakerenclosures with which I am familiar are not as pronounced as in the casewhere the loudspeaker enclosure is arranged for use with a bass or lowfrequency loudspeaker.

This invention provides a loudspeaker enclosure which is remarkably freefrom resonances over the audio frequency range within which it isprincipally used regardless, as a general rule, of the quality or costof the loudspeaker mounted in or to the enclosure. That is, the presentloudspeaker enclosure enables a relatively low cost loudspeaker to beused to reproduce more realistic sound than is obtainable with a higherpriced speaker used in the better of the loudspeaker enclosures nowcommercially available. The present loudspeaker enclosure isstructurally simple, which means that it can be manufactured atreasonable cost. So far as I can ascertain, the present enclosure is notdependent upon critical geometrical relationships although there arecertain geometrical relationships, which I have discovered to beimportant. The present loudspeaker enclosure is usable with a wide rangeof loudspeaker sizes; the important relationships which I havediscovered enable the dimensions of the enclosure to be adjusted tocorrespond to the size of a particular loudspeaker, without significantvariation in the performance of the enclosure from size to size.

Generally speaking, this invention provides a loudspeaker enclosurewhich includes a housing defining therein a principal volume having afront wall. The housing also defines the substantially smaller minorvolume. The minor volume has a rear wall which is common to the frontwall of the principal volume. The common wall between the minor andprincipal volumes defines a port which communicates the two volumeswithin the enclosure. A speaker mounting opening is defined in a frontwall of the minor volume; this opening defines the only opening from theexterior of the housing to the interior.

DESCRIPTION OF THE DRAWINGS

The above-mentioned and other features of this invention are more fullyset forth in the following detailed description of presently preferredembodiments of the invention, which description is presented withreference to the accompanying drawing, wherein:

FIG. 1 is a perspective view of a loudspeaker enclosure according tothis invention; and

FIG. 2 is a cross-sectional elevation view of the enclosure.

DETAILED DESCRIPTION

A loudspeaker enclosure 10 according to this invention is shown in FIGS.1 and 2. The enclosure is comprised of a housing 11 which has a majorpart 12 and a minor part 13. The housing major part 12 defines aprincipal volume 14 within the enclosure, whereas the housing minor part13 defines a minor chamber 15 in the enclosure. The housing major parthas a front wall 16 on which the housing minor part is constructed andmounted. Enclosure principal chamber 14 is completely sealed from theexterior of the enclosure, save for the presence in front wall 16 of anopening 17 which communicates to the enclosure minor volume. Theenclosure minor volume, in turn, is completely sealed, save for thepresence of opening 17 in its rear wall which is common to the housingprincipal part, and save for the presence in a front wall 18 thereof ofa speaker mounting opening 19.

In use of the enclosure, a loudspeaker 20 is mounted in an airtightmanner to the front wall of the housing minor part, preferably in afront mounting mode in which the rear surface of a speaker mountingflange 21 is engaged with the exterior surface of wall 18. Theengagement of the loudspeaker to wall 18 is made in an airtight mannerby a gasket which typically is provided on a rear face of the mountingflange 21. I prefer to use a front mounting mode of speaker 20 toenclosure 10, as currently recommended by loudspeaker manufacturers. Ihave found, however, that a rear mounting of the loudspeaker to theenclosure is also acceptable. A rear mounting mode is one in which thefront face of flange 21 is engaged with the rear face or surface ofenclosure wall 18.

Housing major part 12 has a width A (see FIG. 1), a depth B, and aheight C. The housing minor part has a width D, a depth E, and a heightF. Opening 17 has a dimension G, and the speaker mounting opening inwall 18 has a diameter H. The thickness of the material from which theenclosure is constructed is indicated in FIG. 2 by dimension I. Actualvalues for all of these dimensions for various sizes of loudspeakerenclosures, all constructed according to this invention, are set forthin Table I in which the dimensions and various relationships thereof arealigned in columns for different loudspeakers nominally sized at 8, 10,12 and 15 inches, according to current practice among loudspeakermanufacturers.

In all of the enclosures to which Table I pertains, the inner surfacesof the principal chamber 1 were covered with a one-inch thickness offiberglass padding. In all cases, the opening 17 between the principaland minor volumes of the enclosure was centered in the front wall of theprincipal enclosure, and the minor volume of the enclosure was centeredrelative to opening 17. In all cases, speaker mounting opening 19 wascentered in wall 18. In each of the enclosures to which Table Ipertains, the principal and minor volumes of the enclosures were ofgenerally rectilinear or cubical configuration. All of these enclosureswere constructed of particle board assembled by gluing and by woodscrews.

In all of the enclosures described in Table I, opening 17 was square andhad the same area as the internal vertical area of minor chamber 15;this is my present preference. However, opening 17 can have a smallerarea than chamber 15 or can be circular in shaped, if desired.

                                      TABLE I                                     __________________________________________________________________________    Table                                                                             Enclosure                                                                             LOUDSPEAKER SIZE (Nominal)                                        Item                                                                              Parameter                                                                             8 in.  10 in. 12 in. 15 in.                                       __________________________________________________________________________    1   A       16.0                                                                             in. 20.0                                                                             in. 22.0                                                                             in. 29.0                                                                              in.                                      2   B       12.0                                                                             in. 12.0                                                                             in. 18.0                                                                             in. 17.0                                                                              in.                                      3   C       16.0                                                                             in. 20.0                                                                             in. 22.0                                                                             in. 29.0                                                                              in.                                      4   D       10.5                                                                             in. 13.0                                                                             in. 14.5                                                                             in. 19.25                                                                             in.                                      5   E       6.75                                                                             in. 6.75                                                                             in. 6.75                                                                             in. 10.0                                                                              in.                                      6   F       10.5                                                                             in. 13.0                                                                             in. 14.5                                                                             in. 19.25                                                                             in.                                      7   G       9.0                                                                              in. sq.                                                                           11.5                                                                             in. sq.                                                                           13.0                                                                             in. sq.                                                                           17.0                                                                              in. sq.                                  8   H       7.125                                                                            in. 9.0                                                                              in. 11.0                                                                             in. 14.0                                                                              in.                                      9   I       3/4                                                                              in. 3/4                                                                              in. 3/4                                                                              in. 1-3/16                                                                            in.                                      10  H/G     0.792  0.783  0.846  0.826                                        11  G/C     0.563  0.575  0.591  0.586                                        12  (D.E.F/A.B.C)                                                                         0.218  0.216  0.146  0.235                                            Internal                                                                  13  (G Area/A.C)                                                                          0.249  0.260  0.274  0.270                                        __________________________________________________________________________

In another enclosure according to this invention, similar to but not oneof those enclosures listed in Table I, a twelve-inch loudspeaker wasfront-mounted to the front wall of a minor chamber having externaldimensions of 13.5 inches high×13.5 inches wide×6 inches deep. Opening17 in this enclosure was 12 inches square so as to make chamber 15 fullyopen to chamber 14. The principal chamber of the enclosure had overalldimensions of 22 inches high×22 inches wide×17 inches deep. The rearwall of the principal chamber was covered by a layer of fiberglassacoustical packing to a depth sufficient to leave a space of from 5 to 6inches behind the front wall 16 of the principal chamber, as shown inFIG. 2 by packing material 22, the forward face of the packing materialwas covered by an impermeable membrane 23.

The data set forth in Table I (see Item No. 12) indicates that therelative volumes of the principal and minor chambers of the enclosuremay vary rather substantially in relative size.

The reasons why loudspeaker enclosures, constructed as described above,have such significantly improved freedom from resonance is notunderstood. The absence of the resonances in the enclosures describedabove in the range of from 10 to 100 hz is believed to be particularlysignificant. It is in this range that the prior bass loudspeakerenclosures known to me exhibit significant objectionable resonance.

The loudspeaker network with which an enclosure of this invention isused can be adjusted to have the bass speaker rolloff frequencies at anyfrequency desired. My preference with the nominal 12 inch loudspeakerenclosure described above is to provide roll-off below about 25 to 30 hzand above about 60 to 80 hz.

The foregoing description has been made with reference to certainspecific enclosure structures which are the enclosure arrangements whichI presently prefer. Persons skilled in the art to which this inventionpertains will understand that the principles of my development can beadapted in enclosures of different specific arrangement. Therefore, theforegoing description is principally illustrative and should not beregarded as restricting this invention in scope only to the particularenclosures which have been described.

What is claimed is:
 1. A loudspeaker enclosure comprising a housingdefining therein a principal volume having a front wall .Iadd.providinga front boundary of the principal volume .Iaddend.and a substantiallysmaller minor volume having a rear . .wall.!. .Iadd.boundary.Iaddend.common to the front . .wall.!. .Iadd.boundary .Iaddend.of theprincipal volume, . .the common.!. .Iadd.said front .Iaddend.walldefining a port communicating the minor volume only to the principalvolume, .Iadd.the principal volume front boundary having selected heightand width dimensions, the principal volume also being of selected depthin a direction perpendicular to its front wall, the minor volume at itsrear boundary having height and width dimensions which are less than andare in directions respectively parallel to the height and widthdimensions of the principal volume front boundary, .Iaddend.and aspeaker mounting opening defined in a front wall of the minor volume,the mounting opening defining the only opening from the exterior of thehousing to the interior thereof, and in which the speaker mountingopening opens essentially directly from the interior of the enclosure tothe exterior thereof.
 2. A loudspeaker enclosure according to claim 1wherein the minor volume is substantially centered on the front wall ofthe principal volume.
 3. A loudspeaker enclosure according to claim 1wherein the port is substantially centered in the rear . .wall.!..Iadd.boundary .Iaddend.of the minor volume.
 4. A loudspeaker enclosureaccording to claim 1 wherein the minor volume is substantially centeredon the front wall of the principal volume and the port is substantiallycentered in the front wall of the principal volume.
 5. A loudspeakerenclosure according to claim 1 wherein the ratio of the minor volume tothe principal volume is in the range of from about 0.120 to about 0.250.6. A loudspeaker enclosure according to claim 1 including a quantity ofacoustical packing material in the principal volume over the area of arear wall of the principal volume and extending at least partiallytoward the principal volume front wall.
 7. A loudspeaker enclosureaccording to claim 6 wherein the packing material extends only partiallytoward the principal volume front wall, and including a membranesubstantially impermeable to air disposed across the surface of thepacking material adjacent said front wall.
 8. A loudspeaker enclosureaccording to claim 1 wherein the principal volume is of generallyrectilinear configuration.
 9. A loudspeaker enclosure according to claim1 wherein the minor volume is of generally rectilinear configuration.10. A loudspeaker enclosure according to claim 1 wherein the principaland minor volumes are both of generally rectilinear configuration.
 11. Aloudspeaker enclosure according to claim 1 wherein the minor volume hasall dimensions thereof smaller than the corresponding dimensions of theprincipal volume.
 12. A loudspeaker enclosure according to claim 1wherein the ratio of the area of the port to the area of the principalvolume front . .wall.!. .Iadd.boundary .Iaddend.is in the range of fromabout 0.24 to about 0.28.
 13. A loudspeaker enclosure according to claim1 wherein the ratio of the diameter of the speaker mounting opening tothe diameter of the port is in the range of from about 0.75 to about0.90. .Iadd.
 14. A loudspeaker enclosure comprising for each loudspeakermountable to the enclosure, a primary chamber defining a principalinterior volume and a secondary chamber defining a minor interior volumesubstantially smaller than the principal interior volume, the primarychamber having a front wall with outer and inner faces, the inner faceforming a front boundary of selected height and width dimensions for theprincipal volume, the secondary chamber being defined by an elongatedhousing essentially permanently sealed to the front wall of the primarychamber and projecting beyond one of the faces of the primary chamberfront wall, said housing defining a speaker mounting opening which opensessentially directly to the exterior of the enclosure from a frontboundary of the minor volume, said housing defining a second simpleopening disposed substantially coaxial with the speaker mounting openingat a rear boundary of the minor volume and which opens through the minorvolume rear boundary to the principal volume, the second openingproviding simple and direct communication between the principal andminor volumes, the minor volume at the second opening having height andwidth dimensions which are less than and are in directions respectivelyparallel to the height and width dimensions of the principal volumefront boundary. .Iaddend. .Iadd.
 15. A loudspeaker enclosure comprisinga housing, the housing being comprised, for each loudspeaker mountableto the enclosure, of a principal chamber structure defining therein aprincipal interior volume of the enclosure and having a front walldefining therein a first simple opening, the principal volume front wallforming a principal volume front boundary having selected dimensions ofheight and width, the housing also being comprised of a minor chamberstructure defining therein a minor interior volume of the enclosurewhich is substantially smaller than the principal volume, the minorchamber structure being essentially permanently mounted to the principalstructure front wall in association with the first opening, the minorchamber structure defining a second simple opening substantially coaxialwith the first opening, the one of the first and second openings whichis most outwardly of the principal volume comprising a speaker mountingopening which opens essentially directly from the interior of theenclosure to the exterior thereof and which is the only opening from theinterior of the housing to the exterior thereof, the minor chamberstructure being so mounted to the principal structure that the principaland minor volumes are in direct and simple communication with each otheronly via the other of the first and second openings, said other of theopenings defining a rear boundary of the minor volume at which the minorvolume has dimensions of height and width which are less than and aredirections respectively parallel to the height and width dimensions ofthe principal volume. .Iaddend.